System for the dynamic multiplexing of digital streams

ABSTRACT

A method and apparatus are provided for the dynamic multiplexing of digital streams which are transmitted in the form of stream units in one channel, each of said stream units bearing a stream identifier which can be used to associate same with the corresponding digital stream. The allocation of an identifier to a digital stream is defined by an allocation table and can vary over time, in such a way as to enable dynamic multiplexing. The aforementioned allocation table bears a version number and, in order to indicate that a change in the version of the allocation table applies to a given digital stream, a burst is transmitted with at least one version change stream unit comprising the current identifier of said digital stream, an indicator which can be used to determine if the stream unit is a version change stream unit and the version number becoming applicable to said digital stream.

CROSS-REFERENCE TO RELATED APPLICATION

This Application is a Section 371 National Stage Application ofInternational Application No. PCT/FR03/01370, filed Apr. 30, 2003 andpublished as WO 03/094531 on Nov. 13, 2003, not in English, which isbased on French application No. FR 02/05605, filed May 3, 2002.

The field of the invention is that of the transmission and broadcast ofdigital streams, in particular for multimedia applications.

More specifically, the invention relates to a method for the dynamicmultiplexing of digital streams, as well the corresponding signal,multiplexing device and receiver.

The invention, in particular, can be applied to the field ofbroadcasting of MPEG2 (Motion Picture Coding Experts Group,) MPEG4, DVB(Digital Video Broadcast,) etc. type multimedia data.

BACKGROUND OF THE INVENTION

Today it is a frequent occurrence, in particular in view of obtainingsavings in terms of bandwidth, to multiplex different digital streamswithin the same signal.

Such multiplexing can be predetermined and its structure is thereforeconstant over time.

Multiplexing can also be dynamic; that is, that the structure of themultiplexed signal changes over time. In this case, a configurationtable, which is part of the multiplex signalling, is generally defined.It can be transmitted by the same transmission channel as the multiplex(called “in-band” signalling) or any other means, for example, by aspecific channel, called a signalling channel, which is distinct fromthe data channel through which the desired digital streams aretransported (called “out-of-band” signalling.)

Thus, within the framework of the MPEG4 standard, a configuration table(or allocation table) called FlexMuxChannelTable indicates to whichdigital stream a specific stream unit is associated, based on its index.Such an index, written in a specific field of the stream unit, isencoded over 256 bits. For example, for a given configuration table,index 112 can correspond to an audio stream, and index 118 to a videostream.

When a stream unit is received, the receiver queries theFlexMuxChannelTable configuration table and determines, according to thestream unit index, the processing that will be applied to it: in theprevious example, the FlexMuxChannelTable table indicates to thereceiver that the stream unit of index 118 must be transmitted to avideo decoder.

Within the framework of applications that operate in “multicast” mode,such an allocation table is sent periodically (for example, once persecond within the framework of Internet type applications,) so that itcan be quickly available for a user that has just connected.

In the framework of dynamic multiplexing, a new allocation table is sentwhenever a change takes place in the multiplex configuration. Thereceiver uses at each instance the last configuration table received todetermine the processing to apply to a specific stream unit.

Nevertheless, this method has the inconvenience of not being veryrobust. Indeed, if loss or an error occurs during the allocation tabletransmission, the processing performed by the receiver is incorrect.Using again the example given above within the framework of MPEG4, thereceiver can thus switch the stream unit of index 118 to a videodecoder, whilst the new configuration table, which it has not receiveddue to a network disturbance, shows that index 188, corresponds to ascene description.

Such losses or deterioration of bursts is frequent, in particular withinthe framework of network transmissions, which are subject todisturbances.

SUMMARY OF THE INVENTION

The aim of the invention is especially to overcome these inconveniencesof the prior art.

More specifically, a purpose of the invention is to provide a robusttechnique of dynamic multiplexing of digital streams that is resistantto possible disturbances in the transmission environment.

Another purpose of the invention is to implement such a technique sothat it is accurate in terms of configuration changes and cost-effectivein terms of pass band (or bandwidth).

Another purpose of the invention is to provide a technique that allowsindependence from the various multiplexed streams with respect to theinstant the configuration is changed.

These purposes, as well as others that will be described below, areobtained with the help of a dynamic multiplexing method of digitalstreams transmitted in the form of stream units in a single channel.Each of these stream units carries a stream identifier that allowsassociating it to the corresponding digital stream, the allocation of anidentifier to a digital stream being defined by an allocation table andbeing able to vary over time to allow dynamic multiplexing.

According to the invention, this allocation table bears a version numberand, to indicate a change in the version of said allocation tableapplies to a given digital stream, a burst is sent with at least oneversion change stream unit that includes:

-   -   the current identifier of said digital stream;    -   an indicator that allows determining that the stream unit is a        version change stream unit;    -   the version number that becomes applicable for said digital        stream.

Thus, the invention is based on an approach that is completely new andinventive for the dynamic multiplexing of digital streams. Indeed, theinvention is based on the introduction, on the one hand, of a versionnumber of the configuration table, and on the other, of fictitiouscontent elements, called version change stream units, which carry theversion number of the multiplex configuration table. These fictitiouscontent elements also bear the current identifier of the digital stream,and enable the various multiplexed streams to change configurationindependently from each other. Furthermore, these version change streamunits are only used during the transition phases of the change inconfiguration, so that the method of the invention is not a largeconsumer in terms of pass band (or bandwidth).

Preferably, said burst includes at least two consecutive version changestream units.

Thus, the risks inherent to the loss or deterioration of the versionchange stream unit are reduced, which makes the dynamic multiplexingmethod of the invention more robust.

Advantageously, said burst includes a sufficient number of consecutiveversion change stream units to cover a predetermined disturbance windowduring which it is possible that no stream units are received correctly.

Thus, the problem of packet (or burst) loss or deterioration in case ofdisturbances in the network or in the transmission channel isalleviated, and it is ensured that in the case of a change inconfiguration, the receiver is always aware of the version number of theallocation table to be used. Indeed, at least one version change streamunit is received before the beginning of the disturbance window and/orafter the end of this window.

In an advantageous embodiment of the invention, said disturbance windowis included between 0.2 and 1 sec.

More generally, the duration of the disturbance window depends on thenetwork characteristics, and the length of the burst is therefore fixed.

Preferably, said indicator is a field that specifies the length of thedesired section of the stream unit (or utilised section). This value, bydefinition, equals zero when a version change stream unit is involved.

The version change stream unit therefore has the same structure as astream unit that can be qualified as a desired or informative streamunit, but it can be easily detected by the receiver, through theindication in the corresponding field, that such a stream unit has anull length. A “real” content element cannot have a null length, so thereceiver directly deduces that the content element is a fictitiouscontent element, indicative of a version change of the configurationtable.

According to an advantageous characteristic of the invention, in aversion change stream unit, the version number is written in theutilised section of said stream unit.

Thus, the structure of informative stream units is used, and inparticular, the field reserved for the utilised section of the contentelements, to insert the version number of the allocation table that mustbe used for the digital stream in question: This way, the version changestream units have the same structure as the information stream units andcan be transported within the multiplex, in the same channel.

Preferably, at least in a transition phase after the transmission ofsaid burst, at least one other version change stream unit istransmitted.

Thus, a version change stream unit can be inserted between twoinformative stream units in order to indicate the version number of theconfiguration table that must be taken into account for the first notnull length stream unit received after the version change stream unit.

According to a first advantageous variant, said allocation table istransmitted in said channel.

This is referred to as “in-band” transmission.

According to a second advantageous variant, said allocation table istransmitted by a distinct path of said channel.

This is referred to as “out-of-band” transmission.

Preferably, said allocation table is transmitted at least two timesbefore becoming applicable for at least one of said streams.

Thus, there is an increased probability that the receiver will receivethe new configuration table, before a version stream change unitindicates that it is applicable for at least one of the digital streams.This contributes to the robustness of the dynamic multiplexing method ofthe invention.

Advantageously, a version change is applied from the first stream unitof the stream in question received after said burst.

Preferably, said streams belong to a group that includes:

-   -   natural audiovisual signals;    -   synthetic audiovisual signals;    -   two-or three-dimensional scenes;    -   descriptive information of the data (often called metadata;)    -   access and permission protection data.

Advantageously, such a method is implemented in MPEG4 or MPEG2 typeapplications.

The invention also relates to a signal that dynamically multiplexes thedigital streams transmitted in the form of stream units in one channel.Each of these stream units carries a stream identifier that allowsassociating it to the corresponding digital stream. The allocation of anidentifier to a digital stream is defined by an allocation table and canvary over time, in order to allow dynamic multiplexing.

According to the invention, this allocation table carries a versionnumber and, to indicate that a version change of said allocation tableapplies to a given digital stream, such a signal includes a burst withat least one version change stream unit that includes:

-   -   the current identifier of said digital stream;    -   an indicator that allows determining that the stream unit is a        version change stream unit;    -   the version number that becomes applicable for said digital        stream.

Preferably, said indicator is a field that indicates the length of thedesired section (or utilised section) of the stream unit. This value, bydefinition, equals zero when a version change stream unit is involved.

Advantageously, said signal is transported over a data channel thatallows transmitting desired stream units, distinct from a signallingchannel that allows transmitting signalling data. Said version changestream unit has the same structure as that of said desired stream unitsand is transported by said data channel.

The version change stream unit therefore makes up a fictitious contentelement that has the same structure as a desired or informative streamunit, and is transmitted by the same channel as the latter, not by adistinct signalling channel. The fields reserved for the length and thedesired section of the stream unit include, respectively, in the case ofa version change stream unit, the null value (to indicate that afictitious content stream unit is involved) and the version number ofthe allocation table applicable for the stream in question.

Preferably, such a signal is implemented by the dynamic multiplexingmethod describe above.

The invention also relates to a dynamic multiplexing device for digitalstreams transmitted in the form of stream units in one channel. Each ofthese stream units carries a stream identifier that allows associatingit to the corresponding digital stream. The allocation of an identifierto a digital stream is defined by an allocation table and can vary overtime in order to allow dynamic multiplexing.

According to the invention, said allocation table carries a versionnumber and, to indicate that a version change of said allocation tableapplies to a given digital stream, a burst of at least one versionchange stream unit is transmitted. This burst includes:

-   -   the current identifier of said digital stream;    -   an indicator that allows determining that the stream unit is a        version change stream unit;    -   the version number that becomes applicable for said digital        stream.

Preferably, such a device implements the dynamic multiplexing methoddescribed above.

Advantageously, such a device feeds the transmission means:

-   -   over the Internet; and/or    -   over a DVB network.

The invention also relates to a receiver of a signal multiplexedaccording to the dynamic multiplexing method described above.

Advantageously, such a receiver includes means for detecting said burst,and means for activating the corresponding version change over thestream in question.

Other characteristics and advantages of the invention will become moreevident upon reading the following description of a preferredembodiment, given by way of a simple illustrative and nonexhaustiveexample.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates a block diagram of an MPEG4 type application platformto which the dynamic multiplexing method of the invention can beadvantageously applied;

FIG. 2 illustrates the version change of an allocation table that can,for example, be implemented within the framework of the applicationplatform in FIG. 1;

FIGS. 3 a and 3 b describe the compared structure of a desired orinformative stream unit and a version change stream unit according tothe invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

The general principle of the invention is based on the introduction, onthe one hand, of an allocation table version number and, on the other,fictitious content elements that indicate a version change, for a givendigital stream.

Presented, in reference to FIG. 1, is an embodiment of the inventionwithin the framework of an MPEG4 type application platform.

The architecture of such a platform is a classical architecture of theMPEG4 standard, and will therefore be described briefly below. For moreinformation, the reader can refer to the MPEG-4 system standard (ISO/IEC14496-1.)

Block 1 constitutes a database that stores a plurality of MPEG4 typefiles and allows generating a plurality of related digital streams,which the invention allows to dynamically multiplex.

During transmission, the invention is more specifically implemented inthe block referenced as 2 for synchronising and multiplexing the variousdigital streams. Within the framework of the MPEG4 standard, thismultiplexing block 2 uses a Flexmux multiplexing tool. The output of theFlexMux tool is done in real time towards block referenced as 4 or indeferred time towards block referenced as 3 for storage (the variouscorresponding FlexMux files are therefore stored in reference block 3.)Thus, the MPEG4 system layers are used to multiplex and synchronise theMPEG4 audio and video streams and, for example, MPEG7 data that describethe segmentation of objects in MPEG4 video, and that describe the linksattached to the various segmented video objects.

The digital multiplex crosses an RTP (Real Time Transfer) network layerreferenced as 4, then passes, via the IP (Internet Protocol) network 5,up to the block referenced as 6, where it is processed, with respect tothe FlexMux files 7 stored locally, using the Transmux tool 8 of theMPEG4 standard, which ensures the comprehension of the RTP protocol forextracting MPEG-4 signals.

During reception, the invention is more specifically implemented in theblock referenced as 9, where the multiplex received is demultiplexed inorder to generate a plurality of audio, video, scene description or evenmetadata elementary streams 10 ₁, 10 ₂, 10 ₃, 10 ₄. These variousdigital streams are then processed by block 11, according to theirnature and destination.

Presented now with respect to FIG. 2, is the structure of the multipleximplemented within the framework of the invention, which includesversion change stream units that allow temporally independent changes ofversions for various contents or digital streams.

For simplification, considered is a multiplex 20 of two digital streamsrespectively called content “A” and content “B.” It will be easilyunderstood that the multiplexes implemented within the framework of theinvention generally include a number of digital streams that are greaterthan 2.

The signalling data 21 can be sent out-of-band or in-band. Inparticular, they include packets 22 ₁ to 22 ₃ transporting aconfiguration table (or allocation table) 23 ₁, its version number 23 ₂,as well as the version number 23 ₃ of the current configuration table.

Multiplex 20 includes, for content “A” (respectively, for content “B”,)a plurality of informative or desired stream units referenced as 24 ₁ to24 ₇ (respectively 25 ₁ to 25 ₅.)

According to the invention, to indicate that the configuration tableapplicable for content “A” (respectively “B”) will change (in theexample in FIG. 2, passage of the allocation table of the version numberi to the allocation table of version number i+1,) a burst 28(respectively 29) is sent of fictitious content elements, or versionchange stream units. It can be noted that the fictitious contentelements 28, 29 are represented on FIG. 2 by packets that are smallerthan the informative stream units 24 ₁ to 24 ₇ and 25 ₁ to 25 ₅, whichsymbolises the fact that these fictitious content elements have a nulllength.

Bursts 28, 29 of the version change stream units indicate that the newallocation table applicable for content “A,” “B” in question carries theversion number i+1.

Thus, for content “A” (respectively “B,”) the information stream units24 ₁ to 24 ₄ (respectively 25 ₁ to 25 ₃) referred to version i of theconfiguration table. The receipt of burst 28 (respectively 29) of thefictitious content elements triggers, for content “A” (respectively “B”)at the instant referenced as 26 (respectively 27,) when the version i+1configuration table begins to take into account the content elementsreferenced as 24 ₅ to 24 ₇ (respectively 25 ₄ to 25 ₅) that will besubsequently received.

It can be noted that instants 26 and 27, in which the applicableconfiguration table changes, are distinct for contents “A” and “B.” Theinvention thus, advantageously, allows obtaining independence from themultiplexed contents with respect to the instant of the change inconfiguration.

The version change of the applicable configuration table for a givencontent is taken into account when the first informative stream unit 24₅, 25 ₄ is received (that is, upon receipt of the first non-fictitiouscontent element.)

It can also be noted that the version number i+1 configuration table 231is sent at several occasions, before sending bursts 28 and 29 of theversion change stream units. This way, the i+1 configuration table canbe decoded before instant 26, 27 in which it becomes applicable.Moreover, the repeated sending of this table increases the probabilitythat it will be correctly received at least once by the receiver, in theface of possible disturbances in the transmission network.

In an embodiment variation of the invention, not illustrated in FIG. 2,at least one fictitious content element is also inserted in the “A”and/or “B” content during the transition phase that follows thetransmission of burst 28 and/or 29. For example, a version change streamunit is inserted between packets 24 ₅ and 24 ₆ to indicate a versionchange of the allocation table.

Chosen preferably is a burst 28, 29 duration greater than the durationof an error burst observed on the network used by multiplex 20. Thisway, the robustness of the multiplexing method of the invention isensured by ensuring that the receiver has been correctly informed of theversion change of the allocation table at instant 26, 27 where the newtable becomes applicable in the face of possible network disturbances.

The multiplexing procedure of the invention described with respect toFIG. 2 has a number of advantages with respect to a more summariseddynamic multiplexing solution, in which it would be enough to associatea version number to the configuration table.

Indeed, the dynamic multiplexing method of the invention is more robust,more accurate and more flexible than a dynamic multiplexing method thatonly associates a version number to the configuration table andaccording to which a receiver would monitor the changes in the versionnumber of the table, so that it only takes into account an allocationtable if its version number is different from the previous table. Such amethod would be, indeed, subject to possible losses or deterioration ofthe allocation table during its transmission. Moreover, the change inconfiguration will be forcibly performed at the same time for all thedigital streams of the multiplex, which does not generally correspond toreal needs.

The multiplexing procedure of the invention also has several advantageswith respect to a dynamic multiplexing procedure that may consist inspecifying, each time a configuration table and its related versionnumber is sent, the version number of the current configuration table.It also presents several advantages with respect to such a procedure,which may be completed, during out-of-band signalling, by an insertionmechanism, in each content element or stream unit, of the version numberof the multiplex configuration table.

Indeed, if each multiplexed content element carried a version number ofthe configuration table of the multiplex, the overload, in terms of sizeand therefore pass band congestion, caused by these version numbers,would be significant. The version number of the allocation table wouldbe, indeed, present in each multiplexed stream unit, in particularduring the long static phases where the multiplex configuration does notchange, and during the change phases of the multiplex configuration,even when the stream unit in question is not affected by such a change.

Furthermore, in the case of in-band signalling, for which the versionnumber must be written on each multiplexed content element would not bemandatory, the taking into account of the configuration change wouldnecessarily occur at the same instant for all the multiplexed digitalstreams, which does not reflect the needs of the multimedia applicationtypes considered.

The dynamic multiplexing method of the invention, in contrast, allowsmultiplexed contents to change configuration, independent of each other,and not all together.

It does not have the inconvenience described above related to theoverload in terms of size that results from the indication of theversion number on the content elements. In contrast, it allowsintroducing version numbers at the stream unit level only duringtransition phases of a real configuration change, and that, only for thecontent elements whose configuration characteristics change.

Indeed, according to the dynamic multiplexing procedure of theinvention, during the change transition phases of the allocation table,the version number of the new applicable configuration table isindicated by fictitious content elements, only for the contentsmultiplexed whose configuration characteristics change, and this, withthe greatest accuracy possible.

Moreover, according to the invention, the version number of theconfiguration table is not indicated during the allocation stabilityphases for the various multiplexed stream units, whether theirconfiguration characteristics have changed or not. Neither is itindicated during the change transition phases of the allocation tablefor the stream units of the multiplex whose configurationcharacteristics do not change.

Consequently, the invention allows, with respect to other moresummarised dynamic multiplexing procedures that may be envisaged, areduction of the overall throughput of the multiplex, an independencewith respect to the instant of configuration change of the multiplexedflows, and the greatest accuracy possible.

Now described, with respect to FIGS. 3 a and 3 b, is the structure ofinformative stream units and version change stream units implemented bythe invention.

The fictitious content elements introduced by the invention have,advantageously, the same structure than that of real content elements,and are transmitted, using the same transmission channel, within themultiplex.

As an example, described below is the case of the stream units suggestedby the MPEG4 standard.

Within the framework of the ISO/14496-1 (MPEG4 system) standard, andmore specifically, in the case of the multiplex called FlexMux, adigital stream unit includes three fields referenced as 30 to 32 andrespectively corresponding to:

-   -   an index 30, generally coded between 0 and 255, corresponding to        the multiplex channel number and allowing to identify the        digital stream in question;    -   length 31 of the packet;    -   desired section 32 of the content element.

The invention suggests introducing fictitious content elements,corresponding to FlexMux packets that do not transport data in theirutilised section 32. Such packets are characterised by the presence ofthe null value in the length field referenced as 31, which makes themeasily detectable by a receiver. They also transport another versionnumber of the allocation table (or FMC table for FlexMuxChannelTable)applicable to the stream indicated by index 30 in their desired section32.

1. A method comprising: dynamically multiplexing, with a dynamicmultiplexing device, at least two digital streams transmitted in theform of stream units in one channel, each of these stream units bearinga stream identifier that allows associating it to the correspondingdigital stream, the allocation of an identifier to a digital streambeing defined by an allocation table and being able to vary over time,in order to allow dynamic multiplexing, said allocation table beingidentified by a version number, wherein, to indicate that a change ofthe version number of said allocation table is applicable to a givendigital stream, a unique, respective burst is transmitted for that givendigital stream with at least one version change stream unit thatincludes: the stream identifier of said given digital stream; anindicator that allows determining that the stream unit is a versionchange stream unit; and a new version number of the allocation tablethat becomes applicable for said given digital stream, wherein at leastone of the digital streams is permitted to have a different versionnumber than another of the digital streams that are multiplexed in thechannel.
 2. The dynamic multiplexing method according to claim 1,wherein said burst includes at least two consecutive version changestream units.
 3. The dynamic multiplexing method according to claim 1,wherein said burst includes a sufficient number of consecutive versionchange stream units to cover a predetermined disturbance window duringwhich it is possible that no stream units are received coffectly.
 4. Thedynamic multiplexing method according to claim 3, wherein saiddisturbance window is included between 0.2 and 1 sec.
 5. The dynamicmultiplexing method according to claim 1, wherein said indicator is afield that indicates the length of a desired section of the stream unit,said value, by definition, being equal to zero when a version changestream unit is involved.
 6. The dynamic multiplexing method according toclaim 1, wherein, in a version change stream unit, the version number iswritten in a desired section of said stream unit.
 7. The dynamicmultiplexing method according to claim 1, wherein in at least onetransition phase following the transmission of said burst, at least oneother version change stream unit is transmitted.
 8. The dynamicmultiplexing method according to claim 1, wherein said allocation tableis transmitted in said channel.
 9. The dynamic multiplexing methodaccording to claim 1, wherein said allocation table is transmittedthrough a distinct path of said channel.
 10. The dynamic multiplexingmethod according to claim 1, wherein said allocation table istransmitted at least two times before becoming applicable for at leastone of said streams.
 11. The dynamic multiplexing method according toclaim 1, wherein a version change is applied from the first stream unitof the stream received after said burst.
 12. The dynamic multiplexingmethod according to claim 1, wherein said streams belong to a group thatincludes: natural audiovisual signals; synthetic audiovisual signals;two or three-dimensional scenes; descriptive information of the data(often called metadata;) access and permission protection data.
 13. Thedynamic multiplexing method according to claim 1, wherein the method isimplemented in an MPEG4 or MPEG2 type application.
 14. A methodcomprising the steps of: dynamically multiplexing, with a dynamicmultiplexing device, at least two digital streams to produce a signaltransmitted in the form of stream units in one channel, each of saidstream units bearing a stream identifier that allows associating it tothe corresponding digital stream, the allocation of an identifier to adigital stream being defined by an allocation table and being able tovary over time in order to allow dynamic multiplexing, said allocationtable being identified by a version number, wherein, to indicate that achange of the version number of said allocation table applies to a givendigital stream, the signal includes a respective burst for that givendigital stream with at least one version change stream unit thatincludes: the stream identifier of said given digital stream; anindicator that allows determining that the stream unit is a versionchange stream unit; a new version number of the allocation table thatbecomes applicable for said given digital stream, wherein at least oneof the digital streams is permitted to have a different version numberthan another of the digital streams that are multiplexed in the channeland transmitting the signal.
 15. The method according to claim 14,wherein said indicator is a field specifying the length of the desiredsection of the stream unit, this value, by definition, being equals zerowhen a version change stream unit is involved.
 16. The method accordingto claim 14, wherein said signal being transported over a data channelthat allows transmitting desired stream units, distinct from thesignalling channel that allows transmitting signalling data, saidversion change stream unit has the same structure as that of saiddesired stream units and is transported by said data channel.
 17. Themethod according to claim 14, wherein the signal is implemented by thedynamic multiplexing method according to claim
 1. 18. Dynamicmultiplexing device comprising: a multiplexer, which multiplexes, atleast two digital streams transmitted in the form of stream units in onechannel, each of said stream units bearing a stream identifier thatallows associating it to the corresponding digital stream, theallocation of an identifier to a digital stream being defined by anallocation table and being able to vary over time in order to allowdynamic multiplexing, said allocation table being identified by aversion number, wherein, to indicate that a change of the version numberof said allocation table is applicable to a given digital stream, thedevice further comprises a transmitter, which transmits a respectiveburst for that given digital stream with at least one version changestream unit that includes: the stream identifier of said given digitalstream; an indicator that allows determining that the stream unit is aversion change stream unit; and a new version number of the allocationtable that becomes applicable for said given digital stream, wherein atleast one of the digital streams is permitted to have a differentversion number than another of the digital streams that are multiplexedin the channel.
 19. Dynamic multiplexing device according to claim 18,wherein the device transmits the digital streams over at least one of:the Internet; or a DVB network.
 20. A receiver comprising: means forreceiving a signal dynamically multiplexing at least two digital streamstransmitted in the form of stream units in one channel, each of saidstream units bearing a stream identifier that allows associating it tothe corresponding digital stream, the allocation of an identifier to adigital stream being defined by an allocation table and being able tovary over time in order to allow dynamic multiplexing, said allocationtable being identified by a version number, wherein, to indicate that achange of the version number of said allocation table applies to a givendigital stream, the signal includes a respective burst for that givendigital stream with at least one version change stream unit thatincludes: the stream identifier of said given digital stream; anindicator that allows determining that the stream unit is a versionchange stream unit; and a new version number of the allocation tablethat becomes applicable for said given digital stream, and wherein saidreceiver further comprises: means for detecting said burst, and meansfor activating the corresponding change of the version number of saidallocation table applicable for said given digital stream, wherein atleast one of the digital streams is permitted to have a differentversion number than another of the digital streams that are multiplexedin the channel.
 21. A method comprising: dynamically multiplexing, witha dynamic multiplexing device, digital streams transmitted in the formof stream units in one channel, each of these stream units bearing astream identifier that allows associating it to the correspondingdigital stream, the allocation of an identifier to a digital streambeing defined by an allocation table and being able to vary over time,in order to allow dynamic multiplexing, said allocation table beingidentified by a version number, wherein, to indicate that a change ofthe version number of said allocation table is applicable to a givendigital stream, a burst is transmitted with at least one version changestream unit that includes: the stream identifier of said given digitalstream; an indicator that allows determining that the stream unit is aversion change stream unit, wherein said indicator comprises a fieldhaving a value that indicates the length of a desired section of thestream unit, said value, by definition, being equal to zero when aversion change stream unit is involved; and a new version number of theallocation table that becomes applicable for said given digital stream.